Coking is a well-known process in the refining industry and its objective is to upgrade heavy cuts and particularly distillation residues by causing them to undergo thermal decomposition.
This generally takes place in large, empty reactors where distillates are produced by decomposition and released from the reactor while coked products are deposited inside the reactor.
The feedstock is usually introduced at the bottom of the reactor and, in this case, the coke is first deposited on the bottom of the reactor; it then fills up the lower parts of the reactor up to a predetermined height.
At this point, feedstock injection is stopped and this feedstock is sent to a second, empty reactor.
After this first coke formation stage, there is a second stage in which the coke produced is recovered.
For this purpose, after all the residual hydrocarbons have been drained from the reactor and it has been cooled, its upper part is opened and a hole is bored with appropriate tools. These are usually supported by a scaffolding or derrick for boring into the reactor from its top. The derrick structure (one per reactor) is installed around the reactors, themselves located well above ground so that the feedstock can be injected and the coke produced can be recovered from the reactor by gravity then conveyed to a storage area or to the consumer.
Patents FR-2,615,198, FR-2,622,596 and FR-26,640,992 of the applicant describe decoking processes and devices that avoid the derricks around the reactors to make the entire structure simpler, reduce investment cost, and render coke extraction more practical and economical. The teaching in these documents consists in a first stage of spraying water under pressure in the direction of the coke vertically downward such as to penetrate the coke layer, and continuing this operation until the decoking tool reaches the bottom of the reactor, then, in a second stage, ejecting the water sideways and simultaneously raising the tool to empty the reactor. Rotation of the tool is effected by tangential reaction of water in a direction comprising a tangential component or by a mechanical system driven by a water flow tapped off the main flow used to cut the coke.
Since coke is a brittle material, the mass of coke around the hole bored by the downward water jets slumps into a compact mass. When the decoking device is raised, the tool may be caught in this compact mass and a substantial pulling force has to be exerted on the shaft supporting the decoking tool to release it and continue the emptying operation with the aid of side jets. This relatively high pulling force leads to deterioration of the decoking tool and the hose.